Antenna for radiating circularly polarized waves



Jan. 425, 1949 P, J, KIB'LER 2,460,260

ANTENNA yFOR RADIATING CIRCULARLY POLARIYZED WAVES Fi led Ocr.. 3, 1945SOURCE OF MODULATED CARRIER WAVE Patented Jan. 25, 1949 ANTENN FRRADIA'NG CIRCULARLY PLRZED tit/'AVES aul il. iililer, Fort Wayne, Ind.,assigner', by mesme assignments, te Farnsworth Research Corporation, acorporation oi indiana Application October 3, l9li5, Serial No. 619,995

This invention relates generally to high frequency antennae, and moreparticularly relates to an antenna system arranged to operate oncircularly polarized waves so that its horizontal field strength patternclosely approaches a circle.

For the transmission of television signals it is conventie-nai practicein this country to radiate a modulated carrier wave which ishorizontally polarized. In England vertical polarization oi a carrierWave modulated by a composite television signal is preia red. However,whether the modulated carrier wave be horizontally or verticallypolarized, interference between the direct ray and a reflected raycannot be eliminated. In general, a carrier Wave reflected from anyplane surface will have its amplitude and phase changed depending uponthe dielectric constant of the reiiecting surface and the angle ofincidence of the wave. As long as the angle of incidence of thereiiected wave is not too large, the phase of a f wave polarized in theplane of incidence remains unchanged upon reflection, while the phase ofa wave polarized perpendicularly to the plane of incidence is reversed.When the angle of incidence exceeds a certain value, which depends uponthe dielectric constant oi the reflecting surface, the phase angle isreversed whether the Wave is polarized in the plane of incidence ornormal thereto.

lt will be appreciated that a modulated carrier wave may be reflected bya horizontal surface, that is by the surface of the earth or by Water,as well as by vertical surfaces, such as buildings and other verticalstructures which may be arranged between the transmitter and thereceiver. Thus, no mattei' Whether a horizontally polarized or avertically polarized carrier wave is transmitted, reflection of the wavewill usually take place, and subsequently the response curve of thereceiver will be a function of the frequency due to the difference inphase between the direct ray and the reiiected ray.

It has been suggested to radiate a modulated carrier Wave which iscircularly polarized. Under usual conditions a circularly polarized wavewill reverse its sense oi rotation upon reecton. It is well understoodin the art that a crcularly polarized wave may be considered as theresultant of two waves polarized linearly in a direction normal to eachother and having a phase difference time of 9i? degrees. Hence, acircularly polarized wave may be considered as being composed oi ahorizontally polarized and a vertically polarized wave. Upon reflectionon a at surface one of the component waves will have its phase re- 5Claims. (Ci. Z50-33.53)

versed, while the phase of the other component wave remains unchangedwith the eiect thatv the sense of rotation of the reflected circularlypolar- Y ized wave yis reversed.

' larized wave in -all horizontal directions.

Thus it is possible to radiate a modulated Vcar-- rier wave which iscircularly polarized and which has a predetermined sense of rotation.When the receiver is arranged to receive only circularly vpolarizedwaves having the predetermined sense -of rotation, a deflected wave willnot be received by such a receiver. The transmission of signals -bymeans ci a circularly polarized carrier wave also has other advantagesas will appear hereinafter.

It is usually desired to radiate a circularly po- However, aconventional antenna system comprising two dipole antennae displaced by90 degrees from eachother and energized with a 90 deg-rees phase shiftwith respect to each other will not radiate a circularly polarized waveuniformly in all horizontal directions. Strictly speaking, a circularlypolarized wave will only be radiated in the direction of a plane.Accordingly, a conventional antenna system can not be used for radiatinga circularly polarized modulated carrier wave into a large area asrequired for the transmission of television signals.

It is furthermore desirable to utilize a directive antenna so that theenergy radiated from the antenna has a maximum in the horizon-taldirection and a minimum in the vertical direction. Thus, a directiveradiating system preferably should have a horizontal eld strengthpattern which approaches a circle so `that a large area may be coveredas uniformly as possible by one transmitting antenna.

vIt is an object of the .present invention, therefore, to provide a highfrequency antenna system suitable for operation on circularly polarizedwaves.

Another object of the invention is to provide a nigh frequency directivelantenna system which will radiate a circularly polarized Wave in allhorizontal directions with a maximum eld strength in the horizontalplane.

A further object of the invention is to provide a high frequencydirective antenna system or antenna array arranged for operation oncircularly polarized waves and having a eld strength pattern in thehorizontal plane which closely ap;- proaches a circle.

In accordance with the present Vimfent-ion, there is provided a highfrequency directive an? tenne. system comprisingA a horizontal Vradiatorincluding a plurality ci conductors arranged horizontally with a commonaxis, connected together at their ends and forming each a peripherallyincomplete loop. One of the conductors is open at its mid point toprovide a pair of terminals. The horizontal radiator has an effectiveelectrical length which is substantially equal to one-half wavelength atthe high frequency. A rst transmission line is connected to theterminals for transfer of high frequency energy between the horizontalradiator and the rst transmission line. There is also provided avertical radiator including a dipole conductor arranged vertically alongthe common axis of the horizontal radiator. The vertical radiator has aneffective electrical length which is substantially equal to one-half thewavelength at the high frequency. Finally, a second transmission line isprovided which is connected to the vertical radiator for transfer ofhigh frequency energy between the vertical radiator and the secondtransmission line.

For a better understanding of the invention, together with other andfurther objects ther of, reference is made to the following description,taken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a perspective view, with partsbroken away, of a high frequency antenna system embodying the presentinvention, while Fig. 2 is a perspective View of an antenna array havingtwo stacked antenna systems in accordance with the invention.

Referring now more particularly to Fig. 1 of the drawing, there isillustrated a high frequency directive antenna system comprising ahorizontal radiator I and a vertical radiator 2. Horizontal radiator Iis essentially a folded half-wave dipole bent into a circle to form twoperipherally incomplete loops or conductors 3 and 4. The open ends ofconductors 3 and 4 are connected together electrically by capacitanceplates 5 and 6. Accordingly, conductors 3 and 4 are capacitance loadedat their ends to secure a more near- 1y uniform current distribution. Asillustrated in Fig. 1, conductors 3 and 4 are arranged horizontally witha common vertical axis along which vertical radiator 2 is arranged.Conductors 3 and 4 have been illustrated as tubes of toroidal shapehaving equal inner diameters. However, it is to be understood thatconductors 3 and 4 may also have different inner diameters and that morethan two conductors may be provided. Conductor 4 is open at its midpoint to form a pair of input terminals 'I which are connected toimpedance matching box 8 by two parallel conductors Ill.

Conductors 3 and 4 with their capacitance plates 5 and 6 form ahorizontal radiator having an effective electrical length which issubstantially equal to one-half the wavelength of the modulated carrierwave to be transmitted or received. Actually the effective electricallength of each loop 3 and 4 is substantially equal to one-half thewavelength of the carrier.

Vertical radiator 2 may consist of a conventional vertical half-Wavedipole. Preferably, however, vertical radiator 2 consists of a so-calledcoaxial vertical dipole or sleeve antenna. Thus, vertical radiator 2includes a coaxial transmission line II comprising center conductor I2and cylindrical conductor i3 coaxial with center conductor I2. Coaxialconductor II may form an extension of a low loss coaxial transmissionline I5. It will be seen that center conductor I2 extends beyondcylindrical conductor I3. Vertical radiator 2 further includes outerconductor I6 in the form of a large pipe or cylinder surroundingcylindrical conductor I 3 and connected at I'I to the free end ofcylindrical conductor I3. Accordingly, cylindrical conductor I3 andouter conductor I6 together form a sleeve oracollar.

The effective electrical length of vertical radiator 2 is alsosubstantially equal to one-half the wave-length of the modulated carrierwave to be transmitted or received. The length of center conductor I2extending beyond cylindrical conductor I3 and outer conductor I5,preferably equals the length of outer conductor I 5, each beingindividually equal in length to one-quarter the wave-length of thecarrier wave to be transmitted or received.

The capacitance formed by plates 5 and 6 may be made adjustable to varythe resonant frequency of horizontal radiator I. Accordingly, it will beseen that the physical length of each loop 3 and 4 will be less thanone-half the wavelength of the carrier wave to be radiated. In somecases it may also be advantageous to provide a capacitance between inputterminals 'I of conductor 4 for adjusting the resonant frequency ofhorizontal radiator I. Vertical radi.. ator 2 should be arranged alongthe common vertical axis of conductors 3 and 4. However, verticalradiator 2 need not be arranged symmetrically with respect to ahorizontal plane passing between conductors 3 and 4.

Vertical radiator 2 is, preferably, connected to a coaxial transmissionline I 5. Horizontal radiator I is connected through impedance matchingbox 8 to parallel wire line 23 shielded by cylindrical conductor 2lwhich is grounded as shown. Impedance matching box S may, for example,

40 consist of a quarter wave transmission line of suitablecharacteristic impedance or of a network consisting of lumped elementsand matches the terminating impedance of parallel wire line 20 and theinput impedance of horizontal radiator l which may be of the order of 35ohms.

Both horizontal radiator I and vertical radiator 2 are connected to asource of a modulated carrier wave indicated schematically at 22.Parallel wire line 20 is directly connected to source 22, while coaxialtransmission line I5 is connected to source 22 through phase shifter 23.Phase shifter 23 is arranged so that the modulated carrier wave fromsource 22 is transferred to vertical radiator 2 with a 90 degrees phaseshift in time with respect to the modulated carrier wave transferred tohorizontal radiator I. Provided the length 0f parallel wire line 20 isequal to the length of coaxial transmission line I5 between source 22and their respective radiators I and 2, phase shifter 23 should shiftthe phase of the modulated carrier wave by degrees. However, theelectrical length of parallel wire line 2B need not be the same as thatof coaxial transmission line i5. In that case phase shifter 23 should bearranged so that the phase of the wave transferred to vertical radiator2 has a 90 degrees phase-shift in time with respect to the phase of thewave transferred to horizontal radiator I.

In order to radiate a circularly polarized wave from the antenna systemof Fig. l, the amplitudes of the waves transferred to horizontalradiator I and to vertical radiator 2 should be equal. Actually, in viewof the fact that the radiation resistance of radiators I and 2 may bedifferent, the Wave radiated from horizontal radiator l should have thesame amplitude as the wave radiated from vertical radiator Horizontalradiator l radiates a horizontally polarized wave into space, whilevertical radiator 2 radiates a vertically polarized wave. Bothhorizontal radiator l and vertical radiator 2 radiate energypredominantly in a horizontal plane.

It is well understood in the art that when a hori zontal radiator is fedwith a wave that is 90 degrees out of phase in time with respect to thatof the wave fed to a vertical radiator, a circularly polarized wave isradiated into space. The eld strength pattern of horizontal radiator lclosely approaches a circle as is well understood in the art.Consequently, the field strength pattern of the antenna systemcomprising horizontal radiator l and vertical radiator 2 will besubstantially uniform in all horizontal directions. Furthermore, theantenna system of the invention will radiate a substantially circularlypolarized wave in all horizontal directions.

The antenna system illustrated in Fig. 1 has been described particularlyas a transmitting ann tenna system. However, it is to be understood thatthe antenna system of Fig. 1 may also be employed with receivingequipment. It is immaterial whether the antenna system of the inventionis used for radiating energy into space or for abstracting energy froman incident high frequency electromagnetic wave.

A transmitting antenna in accordance with the present invention whichradiates a circularly polarized wave substantially uniformly in allhorizontal directions may be used with advantage in a television system.In densely populated areas reections'of the modulated carrier wave frombuildings and other vertical structures cause blurring of the reproducedtelevision picture in View of the difference in time between the directand a reflected wave. This drawback may be substantially eliminated byradiating a circularly polarized wave having a preferred sense ofrotation. Since the sense of rotation of a circularly polarized wave isreversed when the wave is reflected, reception of the reflected Wave maybe prevented by providing a receivercircuit which is only responsive tothe preferred sense of rotation of the circularly polarized wave. A

preferred receiver circuit which is only respon-- sive to circularlypolarized waves having a predetermined sense of rotation is described inUnited States Patent No. 2,359,331, granted on June 6, 1944, to l-I.Salinger, and assigned to thek same assignee as is this application.

When reflection of the received wave from buildings and other verticalstructures is too infrequent to cause appreciable distortion of thereceived signal, a circularly polarized wave may also be used forimproving the signal to noise ratio at the receiver. To this end thereceiver antenna may consist of a conventional half-wave dipole. Thedipole antenna may be oriented in any direction in a plane normal to theline connecting transmitter and receiver without loss of signalstrength. Hence, the receiving antenna may be arranged in a direction sothat the effect of local noise sources isminimized.

The phase and the amplitude of the wave radiated by horizontal radiatori may not be eX- actly equal in all horizontal directions. Accordingly,the wave radiated in certain horizontal directions by the antenna systemof Fig. l may be elliptically polarized instead of circularly polarized.The wave radiated by the antenna sys@V tern or Fig. l is only circularlypolarized when the amplitudes of the modulated carrier wave radiatedfrom horizontal radiator i and vertical; radiator 2 are equal and whenthe phase difference in time between the two waves radiated fromradiators l and 2 is 90 degrees. In order to overcome this drawback, itmay be advantageous to use an'antenna. array such as shown inFig. 2.

Referring now to Fig. 2, in which like cornponen-ts are designated bythe same reference numerals as were used in Fig. i, there is providedanl antenna array comprising two stacked antenna system-s 3S and 3i.Antenna systems 30 and, 3l each comprise a horizontal radiator l and avertical radiator 2 which may be identical to radiators i and 2 of Fig.l. However, input terminals 32 of antenna system 3! are arrangedopposite to input terminalst of antenna system 3l in a vertical planepassing through the common vertical axis of antenna systems 3B and 3l.

Both antenna systems at and Si are connected to modulated carrier source35. To this end parallel wire line 3E, which may be shielded by groundedtube El, interconnects modulated carrier source 35 to horizontalradiator i of antenna system Phase shifter 3.8 coupled to modulatedcarricr source 35 is connected to coaxial transmission line de fortransferring high frequency energy `from source 35 to vertical radiator2 of .antenna system til. Phase shifter 38 is arranged so that the phaseof the high frequency energy transferred to vertical radiator 2 has a 9odegrees phase shift in time with respect to that of the energytransferred to` horizontal radiator i.

The high frequency energy transferred to horizontal radiators i ofantenna systems 3d and 3l' should he in phase, as Well as the energytransferred to vertical radiators 2 of antenna systems Se and 3i.Accordingly, parallel wire line lil, which may be shielded by groundedtube 39, connects modulated carrier source 35 to horizontal antenna i ofantenna system 3l through phase shifter t2. In case parallel wire lines3e and eli have the saine length or differ in length by a fullwavelength of the modulated carrier wave, a phase shifter such as i2 isnot required. Coaxial cable connects modulated carrier source tovertical radiator 2 of antenna system Si through phase shifter 5. Phaseshifter d5 is, arranged so that the energy fed to vertical radiator 2 ofantenna system 3l is 9i) degrees out of. phase in time with respect tothe phase of the energy transferred to horizontal radiator l of entermasystem Sl.'

By arranging input terminals 32 and 33 opposite to each other the slightdifference in phase or amplitude of the wavev radiated by horizontalradiators l in certain horizontal directions is equalized. Accordingly,the wave radiated by the antenna array of Fig. 2 should be circularlypolarized in all horizontal directions with an alcomprising more thantwo stacked antenna n systems such ased and 3l. In that case the inputterminals. such as 32 and 33, of the antenna systemsy shouldbe-'arran-ged symmetrically about the common vertical axis of theantenna systems and in a vertical plane passing through the common axis.In other words, the input terminals of adjacent antenna systems shouldbe arranged opposite to each other. However, for most practical purposesan antenna array comprising two stacked antenna systems, as illustratedin Fig. 2, will be sufficient for radiating a Wave which is circularlypolarized in all horizontal directions with a substantially circularfield strength pattern.

While there has been described what is at present considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fallwithin the true spirit and scope of the invention.

What is claimed is:

J.. A high frequency directive antenna array comprising two stackedantenna systems each having a horizontal radiator including a pluralityof conductors arranged horizontally with a common vertical axis,connected together at their ends and forming each a peripherallyincomplete loop, one of said conductors being open at its mid point toprovide a pair of terminals, said horizontal radiator having aneffective electrical length substantially equal to one-half wavelengthat said high frequency, a first transmission line connected to saidtermina-1s for transfer of high frequency energy between said horizontalradiator and said first line; each of said two antenna systems furtherhaving a vertical radiator including a dipole conductor arrangedvertically along said common axis, said vertical radiator having aneffective electrical length substantially equal to one-half saidwavelength, and a second transmission line connected to said verticalradiator for transfer of high frequency energy between said verticalradiator and said second line, the terminals of said two horizontalradiators being arranged opposite to each other in a vertical planepassing through said common axis.

2. A high frequency directive antenna array comprising two stackedantenna systems each having a horizontal radiator including a pluralityof conductors arranged horizontally with a common vertical axis,connected together at their ends and forming each a peripherallyincomplete loop, one of said conductors being open at its mid point toprovide a pair of terminals, said horizontal radiator having an eiectiveelectrical length substantially equal to one-half wavelength at saidhigh frequency, a rst transmission line connected to said terminals fortransfer of high frequency energy between said horizontal radiator andsaid first line; each of said two antenna systems further having avertical radiator including a coaxial member having a cylindricalconductor and a center conductor extending beyond said cylindricalconductor, a further outer conductor surrounding said cylindricalconductor, said outer conductor being connected to the free end of saidcylindrical conductor, said vertical radiator being arranged verticallyalong said common axis and having an effective electrical s lengthsubstantially equal to one-half said wavelength, and a secondtransmission line connected to said coaxial member for transfer of highfrequency energy between said vertical radiator and said second line,the terminals of said two horizontal radiators being arranged oppositeto each other in a vertical plane passing through said common axis.

3. A high frequency directive antenna array comprising two stackedantenna systems each having a horizontal radiator including a pluralityof closely spaced conductors arranged horizontally with a commonvertical axis, connected together at their ends and forming each aperipherally incomplete loop, one of said conductors being open at itsmid point to provide a pair of terminals, said horizontal radiatorhaving an effective electrical length substantially equal to one-halfwavelength at said high frequency and being so proportioned that itshorizontal eld strength pattern approaches a circle, a firsttransmission line connected to said terminals for transfer of highfrequency energy between said horizontal radiator and said rst line;each of said two antenna systems further having a vertical radiatorincluding a coaxial member having a cylindrical conductor and a centerconductor ex tending beyond said cylindrical conductor, a further outerconductor surrounding said cylindrical conductor, said outer conductorbeing connected to the free end of said cylindrical conductor, saidvertical radiator being arranged vertically along said common axis andhaving an effective electrical length substantially equal to one-halfsaid wavelength, and a second coaxial transmission line connected tosaid coaxial member for transfer of high frequency energy between saidvertical radiator and said second line having l a difference in phase ofsusbtantially 90 degrees in time with respect to the phase of said highfrequency energy transferred between its associated horizontal radiatorand said first line, the terminals of said two horizontal radiatorsbeing arranged opposite to each other in a vertical plane passingthrough said common axis.

4. A high frequency directive antenna array for radiating circularlypolarized waves substantially uniformly in all horizontal directionscomprising a source of high frequency energy, a plurality of stackedantenna systems each having a horizontal radiator including a pluralityof conductors arranged horizontally with a common vertical axis,connected together at their ends and forming each a peripherallyincomplete loop, one of said conductors being open at its mid point toprovide a pair of terminals, said horizontal radiator having aneffective electrical length substantially equal to one-half wavelengthat said high frequency, a first transmission line connected to saidterminals for transferring high frequency energy from said source tosaid horizontal radiator; each of said antenna systems further having avertical radiator including a dipole conl ductor arranged verticallyalong said common axis, said vertical radiator having an effectiveelectrical length substantially equal to one-half said wavelength, asecond transmission line connected to said vertical radiator fortransferring high frequency energy from said source to said verticalradiator, the terminals of said horizontal radiators being arrangedsymmetrically about said common axis and in a vertical plane passingthrough said common axis, and phase shifting means arranged between saidradiators and said source for energizing said array so that the phase ofthe energy radiated from each of said holizontal radiators is equal,while the energy radiated from each of said vertical radiators isdisplaced in phase by substantially degrees in 9 time against the phaseof the energy radiated from said horizontal radiators.

5. A high frequency directive antenna array for radiating circularlypolarized waves substantially uniformly in all horizontal directionscomprising a source of high frequency energy, two stacked antennasystems each having a horizontal radiator including a plurality ofclosely spaced conductors arranged horizontally with a common verticalaxis, connected at their ends and forming each a peripherally incompleteloop, said horizontal radiator having an effective electrical lengthsubstantially equal to one-half wavelength at said high frequency, ashielded parallel wire line for transferring high frequency energy fromsaid source to said horizontal radiator and electrically coupled to oneof said conductors at its mid point; each of said two antenna systemsfurther having a vertical radiator including a, coaxial member having acylindrical conductor and a center conductor extending beyond saidcylindrical conductor, a further outer conductor surrounding saidcylindrical conductor, said outer conductor being connected to the freeend of said cylindrical conduct-or, said vertical radiator beingarranged vertically along said common axis, a coaxial transmission lineconnected to said coaxial member, phase shifting means for connectingsaid source to said coaxial transmission line for transferring highfrequency energy between said source and said vertical radiator having adifference in phase of substantially 90 degrees in time with respect tothe phase of said high frequency energy transferred to its associatedhorizontal radiator, the mid points of the conductors connected to saidparallel wire lines being arranged opposite to each other in a verticalplane passing through said common axis.

PAUL J. KIBLER.

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